The function of the hydraulic components in the closed hydraulic drive system in braking mode has changed in essence. The hydraulic motor performs the function of a pump under the drag of an external load torque, while the pump becomes a motor under the action of high pressure at the suction port. If the mechanical energy and hydraulic energy one-way conversion components are called primary components, then the mechanical energy and hydraulic energy conversion components are called secondary components. In the steering process of the crawler truck, the hydraulic pump motor of the outer hydraulic system always maintains a one-way energy transfer, which is a primary component. The hydraulic pump motor of the inner hydraulic system achieves a two-way energy transfer under different variable pump displacements, which is a secondary component.

The secondary components are characterised by operating in four quadrants. The secondary components in the, quadrant work in the "motor condition", while the, quadrant is the "pump condition". When the inner hydraulic system motor works in the "pump condition" and the hydraulic pump works in the "motor condition", the system absorbs energy from the load side and transmits it to the engine, and vice versa, when the inner system motor returns to the "motor condition Conversely, when the inner system motor returns to "motor service" and the pump returns to pump service, the system outputs energy to the outside through the motor.